An industrial problem which has not yet been solved satisfactorily is the deoiling of sand and rock masses containing mineral oil.
Sand and rock masses containing mineral oil are present in petroleum deposits and usually tenaciously retain the mineral oil contained therein.
Extraction of oil-containing sand or rock masses with low-viscosity organic solvents, such as, for example, benzine, petroleum ether or halogenoalkanes, can be carried out on a small scale without problems, and also has the desired effect.
However, in the case of most inorganic masses which contain mineral oil and which are present, extraction with organic solvents is absolutely impossible to carry out because of the very large amounts of solvents required, the large amounts of energy associated with recovery of the solvents and the unavoidable losses in solvent, which lead to additional pollution of the environment or to separate expenditure on the purification of waste air.
A process has thus been described, at various times, in which sand and rock masses containing mineral oil are washed thoroughly with water in order to expel the mineral oil mechanically.
However, this process does not enable all the mineral oil contained in the masses to be expelled. Rather, by far the major proportion remains, because the water cannot overcome the forces of adhesion between the oil and rock and the capillary forces, generally the so-called retention forces, and makes channels for itself, through which it flows without effect. The main reasons for this are the different surface tensions between the sand or rock and oil on the one hand and water on the other hand, and the differences in the viscosities of oil and water, which are frequently very high. Attempts have therefore already been made to employ surface-active agents, such as, for example, alkanesulphonates and/or thickeners based on water-soluble polymers or on polysaccharide derivatives, as auxiliaries in the water flooding of petroleum deposits (so-called chemical flooding, tertiary extraction).
However, it has been found that such diverse, high requirements have been placed beyond the surface-active effect and thickener effect of chemical agents of this type that the products used hitherto still leave much to be desired.
A particular disadvantage of the auxiliaries known hitherto resides in the fact that they largely lose their effectiveness in the presence of electrolytes. The use of the unlimited supply of seawater for flooding formations containing mineral oil is thus excluded. A deoiling auxiliary is thus required also to be effective in the presence of electrolytes, this requirement being of particularly great importance for the deoiling of offshore oilfields.
As model experiments in which sand or rock packings containing mineral oil are deoiled and which are confirmed in practice show, it is still essential that the washing liquid can readily be injected, that is to say that it changes as little as possible with time as it flows through porous materials and that it also has optimum rheological properties at different shear rates.
If the deoiling auxiliary is used in the oil extraction sector it is necessary that the products are stable and effective for a long period, even at the high deposit temperatures, and do not damage the deposits and are also effective in the presence of a high electrolyte concentration. Precisely in respect of their compatibility with electrolytes and their stability to heat, the polymers which are thus far known, for example from U.S. Pat. No. 2,775,557 and German Patent Specifications 1,300,481 and 2,444,108, and act as thickeners do not yet fulfil the requirements in practice.